The present invention relates to a stationary induction apparatus such as a transformer and a reactor.
In stationary induction apparatuses such as transformers and reactors, when a circuit connected to a stationary induction apparatus is short-circuited, a large short-circuit current is carried through windings configuring the main body of the apparatus, a leakage flux generated due to the short-circuit current is linked with the winding short-circuit current, and thus a large electromagnetic force is applied to the windings. Because of the electromagnetic force application, the stationary induction apparatus is designed so that the windings can withstand the electromagnetic force. With an increase in the capacity of the apparatus, an increase in the electromagnetic force that the stationary induction apparatus has to withstand causes the difficulty of narrowing electric wires with continuously transposed conductors, and this creates problems such as a cost increase due to widened electric wires and an increase in eddy current losses in the windings. Therefore, a wide variety of methods that decrease the amount of materials of electric wires is adopted, including a method that uses half annealed copper wires for electric wire materials instead of typical annealed copper wires and a method that uses a continuously transposed conductor coated with a thermosetting resin in which the coated conductor is wound, heated, and then hardened. These methods adopt methods that reinforce the strength of electric wires using the physical properties of electric wire materials and resins. However, the methods fail to decrease the strength itself that has to be required.
Therefore, Japanese Unexamined Patent Application Publication No. Hei 8-288153, for example, discloses a stationary induction apparatus. In the apparatus, a magnetic ring configured of a magnetic substance is placed at the end parts of windings or near the region around a tap center, the orientation of a leakage flux is changed from the winding radial direction to the winding axial direction, and this enables the orientation of the electromagnetic force applied to the windings to be changed from the winding axial direction to the winding radial direction. The electromagnetic force in the winding radial direction is more easily supportable than the electromagnetic force in the winding axial direction, and this enables a reduction in the cross sectional area of electric wires. At the place where the orientation of the magnetic flux has been changed due to the magnetic ring, eddy current losses produced in the windings are deceased. Placing the magnetic ring in a shield ring reduces an increase in size that is due to the distance of insulation.